638640 has 60 divisors (see below), whose sum is σ = 2147184. Its totient is φ = 170112.

The previous prime is 638633. The next prime is 638663. The reversal of 638640 is 46836.

It is a tau number, because it is divible by the number of its divisors (60).

It is a super-2 number, since 2×638640² = 815722099200, which contains 22 as substring.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 277 + ... + 1163.

2⁶³⁸⁶⁴⁰ is an apocalyptic number.

638640 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 638640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1073592).

638640 is an abundant number, since it is smaller than the sum of its proper divisors (1508544).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

638640 is a wasteful number, since it uses less digits than its factorization.

638640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 906 (or 897 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 27.

The square root of 638640 is about 799.1495479571. The cubic root of 638640 is about 86.1163019956.

The spelling of 638640 in words is "six hundred thirty-eight thousand, six hundred forty".